Inverters: pure- V quasi- sine

[sarabande]

that makes sense. Thanks for the explanation.

B b but, if you expand the horizontal scale (time, i.e. frequency) for a trace from a dodgy inverter, could you see the harmonics - especially the high frequency ones - that cause the trouble ?

(I can borrow a scope from school, and want to fiddle with some "O" level physics of several decades ago !)

 

[whipper_snapper]

I have dozens of small APC UPSs supporting computers, routers, printers etc etc etc. This thread prompted me to look at the waveform they produce. The only mention I could find in their documentation is in the fault finding section:

fault:Connected equipment loses power.

cause: Connected equipment does not accept the step-
approximated sine waveform the unit.

solution:The output waveform is designed for computers and computer-related equipment. It is not designed for use with motor-type equipment.

They rarely run on battery for more than 5 minutes, but I have never had a problem with computers, including MacBooks, or printers.

 

[rickp]

Surely one problem is that we have no measure of how poorly or accurately the quasi-sine-wave units simulate a sinewave? So whilst one 'quasi-sinewave' unit may drive things fine, another one may not because it has a rougher version of a sinewave.

Rick

 

[savageseadog]

[ QUOTE ]
.................. All emergency computer battery supplies are pure sine wave, so that may tell you something.

[/ QUOTE ]
No they're not
It depends on how much you pay. Whether you pay more or not will depend on how critical the application. Sine wave = no problems, Square wave = some possible problems, Something in between ie quasi sine wave = less problems.

One related issue is that the less sine the wave then the greater power there is in higher frequency components. These will tend to cause electromagnetic interferance which could interfere with radio reception.

 

[tobble]

You won't be able to 'see' the harmonics on a 'scope. The upper hamonics combine to form a non-perfect sinusoid. depending on which harmonics you get, the wave will tend to be more 'square' or 'triangular' or something wierd where you have a combination of the two. and or course in practice there'l be lots of noise on the signal causing other effects which may or may not be limited to fuzziness.

If you want to 'see' the harmonics, you'll need to an FFT (Fast Fourier Transform) module, or the ability to do some signal analysis for example in Matlab. This will give you a line representing the proportion of different frequencies. I.e. what you seem to want is a graph with Frequency on the X axis, ratehr tan time. If you have a very smart 'scope it mighthave an FFT function. very interesting tho, please let me know how you get on!